A device that detects an object existing in the vicinity of a vehicle and notifies a driver of the vehicle of the existence of the object has been known. For example, in Patent Literature 1, a millimeter wave radar detects an object existing in a lane in which a subject vehicle is travelling, a right lane or a left lane relative to the travelling lane. When the detected object is located within a notification target area, the millimeter wave radar notifies the presence of the object.